The forkhead gene family, originally identified in Drosophila, encodes a class of transcription factors that are important for embryogenesis and development. The forkhead domain, also referred to as the “winged helix domain”, is a 100 amino acid sequence which forms a variation of a helix-turn-helix such that the target DNA is recognized by an alpha-helix and two large loops or “wings”. The action of transcription factors is essential for proper development since vertebrate development relies on appropriate temporal and spatial expression of genes. Consequently, errors in the action of forkhead transcription factors may help to identify the molecular basis for developmental defects (Gajiwala and Burley, Curr. Opin. Struct. Biol., 2000, 10, 110-116).
One of these forkhead genes, forkhead box O1A (also called FOXO1A, forkhead in rhabdomyosarcoma, forkhead box O1A (rhabdomyosarcoma), forkhead (drosophila) homolog 1, FKHR, FKH1, FKHR/PAX3 fusion gene, and FKHR/PAX7 fusion gene) was identified and cloned in 1993 based on a chromosomal translocation that is frequently found to be overexpressed or amplified in a high proportion of alveolar rhabdomyosarcomas (ARMS) (Davis and Barr, Proc. Natl. Acad. Sci. U.S.A., 1997, 94, 8047-8051; Davis et al., Cancer Res., 1994, 54, 2869-2872; Galili et al., Nat. Genet., 1993, 5, 230-235). Rhabdomyosarcomas are a group of malignant tumors which are the most common soft-tissue sarcoma of childhood, and ARMS is associated with the expression of two fusion proteins: one is a fusion of the transcription factor PAX3 to forkhead box O1A and the second is a fusion of the transcription factor PAX7 to forkhead box O1A. These fusion genes arise from the chromosomal translocation of the gene encoding the transcription factor PAX3, located on chromosome 2, or PAX7 located on chromosome 1, to a position on chromosome 13 adjacent to the forkhead box O1A gene. Intron 1 of the forkhead box O1A gene is rearranged in t(2; 13)-containing alveolar rhabdomyosarcomas (Davis et al., Hum. Mol. Genet., 1995, 4, 2355-2362). The fusion protein resulting from the t(2; 13) translocation contains the N-terminal region of PAX3, including the DNA-binding domains, and the C-terminal transcription activation domain of forkhead box O1A, with truncation of the forkhead DNA-binding domain (Anderson et al., Genes. Chromosomes Cancer, 1999, 26, 275-285).
Diabetes and its complications are a serious problem for the populations of industrialized countries. Generally, this disease results from impaired insulin production from pancreatic β-cells. In type 2 diabetes, a combination of genetic and environmental factors brings about β-cell failure, which results in impaired insulin secretion and activity. In contrast, an autoimmune process destroys β-cells in type 1 diabetes. Since most individuals with type 2 diabetes are insulin resistant, it is commonly thought that the β-cells failure observed in individuals with type 2 diabetes is related to insulin resistance.
The forkhead box O1A protein may play a role in the progression of diabetes as well as several other diseases. Forkhead box O1A is the transcription factor that binds the insulin response element in the insulin-like growth factor binding protein-1 (IGF-BP-1) promoter (Durham et al., Endocrinology, 1999, 140, 3140-3146). It has been observed that insulin also regulates the activity of forkhead box O1A as a transcription factor of glucose-6-phosphatase, a key enzyme in gluconeogenesis (Nakae et al., J. Clin. Invest., 2001, 108, 1359-1367). Nakae et al. showed that Foxo1 controls two important processes in the pathogenesis of type 2 diabetes: hepatic glucose production and β-cell compensation of insulin resistance. The data suggest a common mechanism by which insulin resistance would bring about metabolic alterations that cause type 2 diabetes. Furthermore, Guo et al. (J. Biol. Chem., 1999, 274, 17184-17192) determined that forkhead box O1A stimulates promoter activity through an insulin response sequence. In addition, Guo et al., using a mutant forkhead box O1A, in which phosphorylation sites were mutated to prevent phosphorylation, showed that phosphorylation of forkhead box O1A by protein kinase B is necessary in order for insulin to disrupt transcription of target genes by forkhead box O1A. It has further been shown that forkhead box O1A activity, but not the PAX3/forkhead box O1A fusion protein activity, can also be suppressed by phosphorylation by Akt (del Peso et al., Oncogene, 1999, 18, 7328-7333; Tang et al., J. Biol. Chem., 1999, 274, 16741-16746). From these observations, it appears that forkhead box O1A may contribute to hepatic production of IGFBP-1 and unrestrained gluconeogenesis in Type 2 diabetes because insulin is not able to regulate the activity of forkhead box O1 as a transcription factor of IGFBP-1.
Prior to the present invention, there were no known therapeutic agents that effectively inhibited the synthesis of forkhead box O1A.
The present invention provides compositions and methods for modulating forkhead box O1A expression.